Uncontrolled metal ions, found ubiquitously as solutions or colloidal suspensions in water, create a great diversity of technical problems, as illustrated by scale or precipitate formation in boilers, difficult cleaning of soils from textile fabrics and hard surfaces and metal-catalyzed decomposition of otherwise useful peroxide, perborate or peracid bleaches. Uncontrolled metal ions, especially those of heavy metals, are often significantly toxic, and in consequence, detoxicants and other pharmaceuticals are needed.
Materials capable of addressing such problems are termed "scale inhibitors", "builders", "water softeners", "sequenstrants", "chelating agents", "bleach stabilizers " and so forth, often depending more on their development history and on arbitrary industry convention than on their prime function or mechanism of action. Certain materials, such as the sodium polyphosphates, are so useful in numerous polyvalent metal-ion control applications that labelling them with only one such term seems to deny their truly multi-functional character. On the other hand, the terms "builder" and "water softener" have come to be conventionally associated with those material which are manufactured in great quantity, mostly for binding calcium or magnesium "hardness" in water, while the terms "sequestrant" and "chelating agent" usually connote high-performance materials, less limited in the range of metal ions they will bind, and capable of controlling numerous metal ions, especially those of the transition metals. "Chelating agents", in particular, tend to form co-ordination complexes with polyvalent metal ions in which there are two or more bonds per metal ion, resulting in one or more strongly bonded "chelate rings". Chelating agents or sequestrants are commonly used in small yet effective amounts in premium cleaning and bleaching products. They enhance cleaning/bleaching performance, very probably due to their typically high binding constants with transition metal ions and consequent ability to tightly bind those ions, even in the presence of a builder.
The use of many widely useful materials based on phosphorus, such as the aforementioned polyphosphates, is increasingly limited by a number of government regulations and certain well-known precipitating builder materials, such as sodium carbonate, are recognized as being much more limited than phosphates in their metal-ion controlling capabilities. Moreover, other builders which act by formation of a water-soluble complex (nitrilotriacetate, NTA, for example, binds both calcium and magnesium rather well in this manner) have been developed but are already subJect to regulation; and ion exchange builders, such as zeolite A, bind calcium strongly, but are insoluble.
Today's laundry detergent compositions comprise a wide variety of functional ingredients designed to clean myriad soils and stains from many different types of fabrics and fabric blends. Such functional ingredients include various surfactants and surfactant blends, as well as bleaches and enzymes, and can have various forms. Liquid products are increasingly sought-after. Into such complex formulations, the formulator will usually wish to introduce one or more builders and/or sequestrants so as to achieve superior cleaning. The situation is complicated in that compatibility of the ingredients must be considered, especially in a liquid; moreover the formulator is constrained by various regulations, as noted.
In light of the foregoing, there is a continuing search for chemical compounds which can be used in detergent compositions for broad-brush sequestration of the more commonplace calcium and/or magnesium hardness, as well as (in admixture with conventional builders such as zeolite A) for more specialized purposes, such as iron, copper and maganese sequestration or stabilizing laundry bleaches, e.g., in liquid form. Furthermore, there is a continuing search for metal ion sequestrants, especially those which do not contain phosphorus and are relatively inexpensive.
Accordingly, it is an object of the present invention to provide new compounds, the N,N'-(1-oxo-1,2-ethanediyl)-bis(aspartates), taking a number of forms including the tetraprotic acid, sodium and potassium salts, esters, and stereoisomers thereof. Any N,N'-(1-oxo-1,2-ethanediyl)-bisaspartate compound directly useful as a functional ingredient in detergent compositions, chelating agent compositions, bleaching compositions, builder compositions and other useful compositions provided by the invention is hereinafter identified by its full name or by the acronym "OEDBA". The acronym may be used in abbreviating formulae, e.g., Na.sub.4 (OEDBA) which is a formula abbreviation for tetrasodium N,N'-(1-oxo-1,2-ethanediyl)-bis(aspartate).
Further objects of the invention include providing methods for making OEDBA, providing a method for sequestering metal ions comprising treating aqueous transition metal-ion containing solutions with OEDBA, and providing chelating agent compositions or sequestrant compositions having an effective amount of OEDBA which are generally useful as a chelating agent, sequestrant or (at higher levels) as water-soluble builder, all without need for isolating the pure compound. It is yet another object herein to provide laundry detergent compositions benefitting from the incorporation of OEDBA as a sequestrant or bleach stabilizer/performance enhancer.